1. Technical Field
The field of the currently claimed embodiments of this invention relates to a tool and tool system, and more particularly to a tool and tool system having independent axial and transverse force sensing.
2. Discussion of Related Art
Retinal microsurgery involves complex intraocular surgical procedures to treat retina-related diseases, e.g., epiretinal membrane (ERM), diabetic retinopathy, retinal detachment, and macular holes. During retinal microsurgery, the surgeon inserts long, thin ophthalmic instruments through trocars on the sclera to perform fine manipulation of the delicate eye tissue in a small constrained space (average axial length of the human eye is about 23.5 mm). One challenge to treatment stems from the microscopic dimensions and the fragility of the tissues in the eye. Another challenge derives from the human physiological limitations, such as surgeon hand tremor and fatigue. One of the most formidable technical challenges is the lack of force sensing. Forces exerted in retinal microsurgery are generally well below the human sensory threshold. A previous study [1] has shown that 75% of forces applied during in vitro retinal manipulation in porcine cadaver eyes are less than 7.5 mN, and only 19% of the events at this force level can be felt by the surgeons. Large forces are undesirable and can potentially damage the delicate retina. Incorporating force sensing capability into the ophthalmic instrument can enable quantitative monitoring of force applied during retinal microsurgery. It can be used to provide awareness of sub-tactile tool-tissue forces to the surgeon. The technology can also be incorporated into robotic systems to provide haptic feedback and motion guidance.
There has been considerable work on force sensing for microsurgery, micromanipulation, and minimally invasive surgery (MIS). Menciassi et al. [2] developed a piezo-actuated microgripper with a dimension of 17×0.5×0.4 mm. The microgripper is instrumented with strain gauges for force sensing to provide haptic feedback in microsurgery. Peirs [3] designed a MIS instrument using intensity modulated optic sensors. It provides triaxial force sensing with a resolution of 0.04 N. Seibold et al. [4] utilized a flexure Steward platform with strain gauges to integrate 6-axis force sensing into an actuated MIS instrument. Polygerinos et al. [5] developed a triaxial catheter-tip force sensor for MRI-guided cardiac ablation procedures. Furthermore, various studies have investigated different force sensing techniques, such as piezoresistive strain gauges [6]-[9] and fiber optical sensors [10], [11]. However, these designs cannot be directly applied to retinal microsurgery due to the specific requirements on the force sensing range (≥10 mN), resolution (≤1 mN), and dimensions (≤0.9 mm in diameter). It is also desired that the force sensor is integrated into the distal portion of the tool shaft, typically located inside the eye. Force sensors mounted in the handle of the microsurgical tool [12] cannot distinguish the force exerted at the tool tip and the contact force at the sclerotomy [13]. Therefore, there remains a need for an improved tool and tool system having independent axial and transverse force sensing.